1. Field of the Invention
The present invention relates to a printing screen and a printing process using the same. More particularly, the present invention relates to a method for improving a side-bottom ratio of a fluorescent layer in a plasma display panel and the printing screen used.
2. Description of Related Art
In recent years, with the rapid advancement of microelectronics technology, the information, communication, network technology and the relative industry have also developed. With that trend, the display apparatus, showing words, data, pictures and moving images, has become an indispensable element. Wherein, the plasma display apparatus, with its advantages such as big size, self-luminescence, wide view angle, thinness and full colors, has a great potential of becoming the mainstream flat panel display apparatus in its next generation.
FIG. 1 is a three-dimensional view of a decomposed conventional plasma display panel. As shown in FIG. 1, plasma display panel 100 mainly comprises a front substrate 110, discharge gas (not shown) and a rear substrate 120. The front substrate 110 mainly comprises a substrate 10, an X electrode and a Y electrode, wherein the X and Y electrodes are disposed on the substrate 10 and are covered with a dielectric layer 111 and a protection layer 12. The rear substrate 120 comprises a substrate 20, an address electrode 15, a dielectric layer 17, a rib 30 and a fluorescent layer 21, wherein the substrate 20 is divided into a plurality of discharge chambers 13 by the rib 30. The discharge gas in the plasma display panel 100 is disposed in the discharge chambers 13.
Following the preceding paragraph, the fluorescent layer 21 is disposed over the side wall of the rib 30 and over the dielectric layer 17. When the drive voltage is provided by the X, Y electrodes and the address electrode 15, the discharge gas in the discharge chambers 13 will be transformed into plasma and emit ultraviolet. When the fluorescent layer 21 is irradiated by the ultraviolet, it will emit visible light, whereby the plasma display panel 100 displays images. It can be learned from the foregoing that the thickness and the coating area of the fluorescent layer 21 over the side wall of the rib 30 and over the dielectric layer 17 have great impact on the luminescent efficiency of the plasma display panel 100.
FIG. 2 is a cross sectional view showing a fluorescent layer disposed into a discharge chamber in a conventional printing process. FIG. 3 is a top view of a printing screen used in the conventional printing process of FIG. 2. As shown in FIG. 3, when the printing process of the fluorescent layer 21 is performed, the printing screen with a corresponding shape of the discharge chamber is required. For example, in the plasma display panel 100 (as shown in FIG. 1), the grid-shaped printing screen 300 is used (as shown in FIG.3), because the fluorescent material is disposed into a grid-shaped discharge chamber 13.
As shown in FIGS. 2 and 3, the printing screen 300 is disposed over the rib 30 with each of the ink apertures 302 aligned with each of the discharge chambers 13 during the fabricating process of the fluorescent layer. Next, a fluorescent material, ink liquid 202, is coated over the printing screen 300 when the ink liquid 202 is scraped into the discharge chambers 13 by a scraper through the ink aperture 302 of the printing screen 300. And then in the baking process, the fluorescent layer 21 (as shown in FIG. 1) is formed over the side wall of the rib 30 and over the substrate 20.
In FIG. 2, when the fluorescent ink liquid 202 flows through the ink aperture 302 into the discharge chamber 13, the fluorescent ink liquid 202 first touches the side wall of the rib 30 and then gradually flows into the bottom of the discharge chamber 13. Therefore, the gas 310 in the bottom of the discharge chamber 13 can not be emitted and is enveloped in the fluorescent layer 21. As a result, after the baking process, the fluorescent layer 21 formed in the bottom of the discharge chamber 13 will have uneven film thickness. In other words, the fluorescent layer 21 will not have a good side-bottom ratio, the ratio referring to the thickness ratio of the fluorescent layer 21 to the side wall of the discharge chamber 13. Consequently, the luminescent efficiency of the plasma display apparatus will downgrade.